20.2. Character Set Support

20.2.1. Supported Character Sets

Table 20-1 shows the character sets available for use in the server.

Not all APIs support all the listed character sets. For example, the PostgreSQL JDBC driver does not support MULE_INTERNAL, LATIN6, LATIN8, and LATIN10.

20.2.2. Setting the Character Set

initdb defines the default character set for a PostgreSQL cluster. For example,

initdb -E EUC_JP

sets the default character set (encoding) to EUC_JP (Extended Unix Code for Japanese). You can use --encoding instead of -E if you prefer to type longer option strings. If no -E or --encoding option is given, SQL_ASCII is used.

You can create a database with a different character set:

createdb -E EUC_KR korean

This will create a database named korean that uses the character set EUC_KR. Another way to accomplish this is to use this SQL command:

CREATE DATABASE korean WITH ENCODING 'EUC_KR';

The encoding for a database is stored in the system catalog pg_database. You can see that by using the -l option or the \l command of psql.

$ psql -l             List of databases    Database    |  Owner  |   Encoding     ---------------+---------+---------------  euc_cn        | t-ishii | EUC_CN  euc_jp        | t-ishii | EUC_JP  euc_kr        | t-ishii | EUC_KR  euc_tw        | t-ishii | EUC_TW  mule_internal | t-ishii | MULE_INTERNAL  regression    | t-ishii | SQL_ASCII  template1     | t-ishii | EUC_JP  test          | t-ishii | EUC_JP  unicode       | t-ishii | UNICODE (9 rows)

20.2.3. Automatic Character Set Conversion Between Server and Client

PostgreSQL supports automatic character set conversion between server and client for certain character sets. The conversion information is stored in the pg_conversion system catalog. You can create a new conversion by using the SQL command CREATE CONVERSION. PostgreSQL comes with some predefined conversions. They are listed in Table 20-2.

To enable the automatic character set conversion, you have to tell PostgreSQL the character set (encoding) you would like to use in the client. There are several ways to accomplish this:

• Using the \encoding command in psql. \encoding allows you to change client encoding on the fly. For example, to change the encoding to SJIS, type:

  \encoding SJIS

• Using libpq functions. \encoding actually calls PQsetClientEncoding() for its purpose.

  int PQsetClientEncoding(PGconn *conn, const char *encoding);

  where conn is a connection to the server, and encoding is the encoding you want to use. If the function successfully sets the encoding, it returns 0, otherwise -1. The current encoding for this connection can be determined by using:

  int PQclientEncoding(const PGconn *conn);

  Note that it returns the encoding ID, not a symbolic string such as EUC_JP. To convert an encoding ID to an encoding name, you can use:

  char *pg_encoding_to_char(int encoding_id);

• Using SET client_encoding TO. Setting the client encoding can be done with this SQL command:

  SET CLIENT_ENCODING TO 'value';

  Also you can use the more standard SQL syntax SET NAMES for this purpose:

  SET NAMES 'value';

  To query the current client encoding:

  SHOW client_encoding;

  To return to the default encoding:

  RESET client_encoding;

• Using PGCLIENTENCODING. If environment variable PGCLIENTENCODING is defined in the client's environment, that client encoding is automatically selected when a connection to the server is made. (This can subsequently be overridden using any of the other methods mentioned above.)

• Using the configuration variable client_encoding. If the client_encoding variable in postgresql.conf is set, that client encoding is automatically selected when a connection to the server is made. (This can subsequently be overridden using any of the other methods mentioned above.)

If the conversion of a particular character is not possible -- suppose you chose EUC_JP for the server and LATIN1 for the client, then some Japanese characters cannot be converted to LATIN1 -- it is transformed to its hexadecimal byte values in parentheses, e.g., (826C).

20.2.4. Further Reading

These are good sources to start learning about various kinds of encoding systems.